17:15 〜 18:45
[ACG31-P06] Investigating the multiscale variability of Taiwan extreme precipitation with emphasis on weather types
キーワード：Taiwan, extreme precipitation, weather type
Taiwan is frequently faced with the threats resulting from weather extremes, especially the extreme precipitation events, and is hence ranked as the country most exposed to “multiple hazards” than any other country by the World Bank (Dilley et al. 2005). To mitigate possible impacts caused by hydro-meteorological disasters, it is important for the local meteorologists and disaster prevention professionals to realize the characteristics of and factors leading to extreme precipitation variabilities in multiscale scales in order to implement timely early warning actions for emergence response.
In comparison with other extreme precipitation relevant researches, this study emphasizes how the large-scale circulation variability as well as the diversity of weather types affects the extreme precipitation occurrences in Taiwan. In general, there are four major weather types which favor the occurrences of extreme precipitation in Taiwan, i. e. the Tropical cyclones (TC), fronts , tropical cyclones accompanied by northeasterly monsoon (TC-NE), and diurnal/afternoon convection. Regardless of the specific season, the highest proportion of extreme precipitation events is caused by the TCs. In terms of different seasons, the dominant weather types that causes extreme precipitation occurrences differ. In the Meiyu season (May-June), the frontal type dominates. In the typhoon season (July-September), the TC type dominates, followed by the diurnal/afternoon convection type. Whereas in autumn (October-November), the TC-NE type is the majority. In addition to the seasonal distribution, the interannual variability of the extreme precipitation occurrences related to these weather types are also discussed. In the period of 1993 to 2015, the extreme precipitation occurrence in the typhoon season exhibited noticeable bi-decadal changes, showing an upward trend and then a downward trend after year 2010 or so.
We further examine with more details the extreme precipitation in specific seasons. Two seasons, the autumn and the winter, are exemplified. In comparison with the studies related to the extreme precipitation variability in Meiyu season and/or typhoon season, the extreme precipitation in autumn is less studied. However, it was not uncommon that the northern Taiwan, the windward side under the northeasterly winter monsoon background, suffered from the threats caused by the extreme precipitation events. We selected 187 extreme precipitation events from 41 years of rain gauge observation and investigated their climate variability. In addition to the TC-NE type, two more weather types are identified as the important weather types related to the occurrences of the extreme precipitation in autumn, including the tropical cyclones-related (TC) type and the northeasterly (NE) types. The 41-year-long extreme precipitation occurrence showed significant interannual variabilities in two different timescales. The lower-frequency scale, the 10-11 year period, is related to the Pacific Decadal Oscillation and the higher-frequency scale, the 2-7 year period, is linked to the El Nino-Southern Oscillation. These three weather types differ in their relationships with PDO and ENSO, respectively, and the large-scale circulation characteristics leading to these differences are discussed.
We also investigated the anomalous wet winter (the number three wettest winter in Taiwan since 1982) in the January and February of 2022. The intensity of the precipitation anomaly and the relevant climate variabilities, in both synoptic scale and interannual scale, were further examined. The significant increase in the winter precipitation of 2022 was shown to result from both an increase in rainfall occurrence frequency and an increase in rainfall intensity. Our further analysis showed that the majority of the increase in winter precipitation resulted from frequent rainy systems propagating from South China or the north of South China Sea to Taiwan, which differed significantly from the general winter conditions that the winter monsoon circulation-induced orographic rainfall and frontal-related rainfall predominantly contributed to the winter precipitation in Taiwan. The possible large-scale circulation characteristics leading to such change were analyzed and discussed.
In comparison with other extreme precipitation relevant researches, this study emphasizes how the large-scale circulation variability as well as the diversity of weather types affects the extreme precipitation occurrences in Taiwan. In general, there are four major weather types which favor the occurrences of extreme precipitation in Taiwan, i. e. the Tropical cyclones (TC), fronts , tropical cyclones accompanied by northeasterly monsoon (TC-NE), and diurnal/afternoon convection. Regardless of the specific season, the highest proportion of extreme precipitation events is caused by the TCs. In terms of different seasons, the dominant weather types that causes extreme precipitation occurrences differ. In the Meiyu season (May-June), the frontal type dominates. In the typhoon season (July-September), the TC type dominates, followed by the diurnal/afternoon convection type. Whereas in autumn (October-November), the TC-NE type is the majority. In addition to the seasonal distribution, the interannual variability of the extreme precipitation occurrences related to these weather types are also discussed. In the period of 1993 to 2015, the extreme precipitation occurrence in the typhoon season exhibited noticeable bi-decadal changes, showing an upward trend and then a downward trend after year 2010 or so.
We further examine with more details the extreme precipitation in specific seasons. Two seasons, the autumn and the winter, are exemplified. In comparison with the studies related to the extreme precipitation variability in Meiyu season and/or typhoon season, the extreme precipitation in autumn is less studied. However, it was not uncommon that the northern Taiwan, the windward side under the northeasterly winter monsoon background, suffered from the threats caused by the extreme precipitation events. We selected 187 extreme precipitation events from 41 years of rain gauge observation and investigated their climate variability. In addition to the TC-NE type, two more weather types are identified as the important weather types related to the occurrences of the extreme precipitation in autumn, including the tropical cyclones-related (TC) type and the northeasterly (NE) types. The 41-year-long extreme precipitation occurrence showed significant interannual variabilities in two different timescales. The lower-frequency scale, the 10-11 year period, is related to the Pacific Decadal Oscillation and the higher-frequency scale, the 2-7 year period, is linked to the El Nino-Southern Oscillation. These three weather types differ in their relationships with PDO and ENSO, respectively, and the large-scale circulation characteristics leading to these differences are discussed.
We also investigated the anomalous wet winter (the number three wettest winter in Taiwan since 1982) in the January and February of 2022. The intensity of the precipitation anomaly and the relevant climate variabilities, in both synoptic scale and interannual scale, were further examined. The significant increase in the winter precipitation of 2022 was shown to result from both an increase in rainfall occurrence frequency and an increase in rainfall intensity. Our further analysis showed that the majority of the increase in winter precipitation resulted from frequent rainy systems propagating from South China or the north of South China Sea to Taiwan, which differed significantly from the general winter conditions that the winter monsoon circulation-induced orographic rainfall and frontal-related rainfall predominantly contributed to the winter precipitation in Taiwan. The possible large-scale circulation characteristics leading to such change were analyzed and discussed.